A hiring manager's suggestions from Boston.com's Job Doc blog:

1. Do not use "Resume", "Resume2," or even "Biotech Resume" as the name of your attachment. An employer will receive many such attachments: how can they expect to locate yours easily? The attachment folder in our email program contains multiple files with such titles. It is much better to use "Name_Resume" or a title that will be unique to you.
2. Do not send a resume in the latest version of Word from Vista (acutally, they mean Word 2007, the.docx format--Javed). Save it as an earlier version of Word and then send the attachment, because many companies do not use Vista. Although my company does not use Word for everyday use, we do have it on our email program. However, we cannot open up ".docx" attachments. An alternative may be to send the attachment in two different versions and let the employer open whichever version is best for them. With so many resumes being sent, do not make it difficult to see your resume.
3. Put some kind of statement in the email, with a line saying how you know about the opening and that your resume and/or cover letter is attached. I never open attachments unless I have an idea of what is in them. I have received supposed applications with no email text - only attachments - which I immediately send to the trash.

Some of you may know that my day job is information security, and we absolutely drum it into people that attachments from unknown people should not be opened without reviewing the context of the email.

I have Word 2007, and have occassionally saved files in .docx format by mistake (since it is the default format) and heard back from people who could not open it.

And what can I say about #1.. in a sea of resume.doc, if you want to be picked, use your name in the filename. I recommend firstname_lastname_resume.doc. With modern operating systems the "_" are not strictly necessary, but old habits die hard for me.

So if you are making these mistakes, stopping will increase your chances right away.

Good luck!